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Community and Q&A

Whole-house minisplit system?

user-471779 | Posted in Energy Efficiency and Durability on

Renovating a large existing house I just purchased (8k square feet uggh,) in zone 3. Not getting into details on loads, the house will be tight and well insulated.

I am obsessed with the thought of using a mitsubishi multi split application. Will be using many different inside units, mostly 6k & 9k wall units… attached to mxz-8c outdoor units.

i need help with clarification on a couple of items.

1. minimum capacity of the mxz-8c outdoor unit. So the minimum capacity for cooling is 6000 btu/h on the outdoor unit. So does this mean that the indoor unit will only be able to modulate down to 6k? if two units are calling for cooling at the same time, will they be able to ramp down to 3k each?

2. I am concerned about the maintenance of having 12 indoor wall units. I just started stressing about this. So they recommend cleaning filters every 2 weeks. Even if it is longer than that, I have seen multiple posts about bad smells from units, and I am concerned about some videos I have seen of how to clean indoor coils and blower wheels, hanging a bag and spraying them off etc.. I am not thrilled about the thought of all that. I often am late on changing my return air filters on my current house!

3. The main reason I want to go with the mini splits is for comfort, and not to have ductwork everywhere. I do have an awesome contractor who is preparing a plan for using 3 Carrier greenspeed 25vnao units, each unit zoned with carriers infinity zoning. These are up to 20 seer units and inverter tech. He would use a venting dehumidifier for supply ventilation. Great filtration etc..

4. i was researching using a recouperator, or zhender unit for erv with mini splits, But would like to have them balanced slightly positive because i do have three fireplaces that have to stay, but would have sealed top dampers.

I really like the mxz outdoor units
I am not crazy about all of the zoning controls being accessible in the carrier option.

What are your thoughts about using multiple mvz units inside instead of the carrier alternative? I could essentially zone with those instead of using larger carrier units? So what would your thoughts on having 4 12k btu mvz vs one carrier 4 ton zoned?

Thanks for your consideration,
I need hvac therapy.

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  1. Dana1 | | #1

    1: If only ONE indoor unit is calling for heat/cool, it will be forced to take the full minimum output of the compressor (it's more efficient to run the single head at high speed than to cycle the compressor on/off), if more than one is calling, they'll be able to split the compressor output (So yes, 3K + 3K if two, or 2K + 4K or some other split, depending on where the zones are relative to the temperature setpoints.)

    2: Is there a question here? (Reads like a series of statements.)

    3: Again, is there a question?

    4: ???

    "Not getting into details on loads,...."

    Then you can't expect much in the way of specific answers. Many ways to skin the cat, but the good/ better/best approaches depend quite a bit on the loads.

  2. GBA Editor
    Martin Holladay | | #2

    I agree with Dana: we need a lot more information before we can give advice. But my first reaction is that it doesn't make any sense to use ductless minisplits in a house that requires 12 indoor units.


    1. Your house really doesn't need as many indoor units as you think it does, or

    2. You would be much better off with a conventional ducted forced-air system.

  3. Dana1 | | #3

    But Martin maybe all rooms are west facing with wall to ceiling windows and hellacious cooling loads! :-)

    Mulit-splits with mini-duct cassette zones serving 2-4 nearby rooms can bring the head count down a lot, and can be more efficient than 2-4 heads of ridiculously oversized capacity.

    Load details matter.

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